1. Field of the Invention
The present invention relates to a drive unit which drives, for example, an imaging optical system and a camera. More particularly, the present invention relates to a drive unit which has a preset function for moving, for example, an imaging optical system and a camera to a previously registered position, and relates to a camera system.
2. Description of the Related Art
Regarding a camera platform used in a monitoring camera system and a weather camera system, a preset function for moving a monitoring camera or a weather camera to a previously registered zoomed, focused, tilted or panning position has been proposed. Regarding such a preset function, a simultaneous start/stop function to start/end each operation substantially at the same time has been proposed. If an operation is performed at a certain constant speed, a change rate of an imaging range of an obtained image is constant during panning and tilting operations while a change rate of a field angle with respect to a moved amount varies depending on the position of a zoom lens during a zooming operation. For this reason, even in a preset operation to a certain subject which exists in a field angle, a viewer may have feeling of strangeness, like a subject once disappears from the field angle and then enters again in the field angle during the operation, in an obtained image when zooming, panning and tilting operations are performed at a constant speed.
As a method for preventing this phenomenon, Japanese Patent No. 3496944 discloses an exemplary operation unit for changing the moving speed in panning and tilting operations in accordance with a current field angle. Further, Japanese Patent Laid-Open No. 2007-282069 discloses an exemplary camera platform system which prevents generation of images which causes feeling of strangeness while reducing the amount of calculation by approximating speed curves in panning and tilting in accordance with the change rate of the field angle of zooming.
However, in both the unit disclosed in Japanese Patent No. 3496944 and the system disclosed in Japanese Patent Laid-Open No. 2007-282069, since the panning and tilting speed is changed in accordance with the change in the field angle caused by the zooming operation, the time in which the unit or the system are operated at the maximum speed (which is usually determined for each model) is short. Therefore, if the moved amount by the panning and tilting operations is large, time necessary for the panning and tilting operations becomes long as compared with a case in which the panning and tilting operations are performed at a constant speed. The time necessary for the preset operation then becomes long.